1. Field of the Invention
The present invention relates to an image detection device, and more particularly to an image detection device for detecting an image by accumulating the charges generated by radiating X-rays to a semiconductor layer as the information of the respective pixels constituting an image.
2. Description of the Invention
Recently, radiation image detection devices such as FPDs (flat panel detector) have come into practical use, and each of the detection devices has X-ray sensitive layer formed on a TFT (thin film transistor) active matrix substrate and can directly convert X-ray information into digital data. The FPDs have been in widespread use rapidly because it has a merit in that they can instantly confirm an image and can also confirm a motion picture as compared with imaging plates according to a related art.
First, a radiation image detection device 100′ according to a related art acting as the FPD will be explained using FIGS. 10 and 11. Note that FIG. 11 shows a sectional view taken along the line C-C of FIG. 10.
As shown in FIG. 11, the radiation image detection device 100′ according to a related art is arranged such that a semiconductor film 6′ with electromagnetic wave conductivity is formed on a TFT active matrix substrate 10′ and a bias electrode 7′ is sequentially formed thereon. The bias electrode 7′ is connected to a high-voltage power supply.
The semiconductor film 6′ is an amorphous a-Se film containing selenium as a main component and having a film thickness of 100 to 1000 μm, and when X-rays are radiated to the semiconductor film 6′, charges are generated in the film.
Next, an operating principle of the radiation image detection device 100′ according to a related art will be explained.
When X-rays are radiated from an upper portion of FIG. 11, charges are generated in the semiconductor film 6′. The positive holes in the generated charges are collected to a charge collection electrode 11′ by a bias between a bias electrode 7′ and the charge collection electrode 11′ and accumulated to a charge accumulation capacitance 5′ electrically connected with the charge collection electrode 11′. Since the semiconductor film 6′ generates a different amount of charges according to the amount of the X-rays, the charges according to the image information carried by the X-rays are accumulated to the charge accumulation capacitances of the respective pixels. Thereafter, signals for turning ON a TFT switch 4′ are sequentially applied through scan wirings 101′ shown in FIG. 10, and the charges accumulated in the respective charge accumulation capacitance 5′ are fetched through data wirings 3′.
Incidentally, this type of the radiation image detection device 100′ has a problem in that since a trap is generated in the semiconductor film 6′, the generated charges cannot be collected well by the charge collection electrode 11′ and thus sensitivity is deteriorated. Further, when X-rays are incident on the device 100′, a phenomenon called ghosting may occur by which the sensitivity is deteriorated according to the incident intensity of the radiated X-rays and takes long time for recovery.
To cope with the above problem, Japanese Patent Application Laid-Open (JP-A) No. 2004-33659 discloses a technology for suppressing the deterioration of the sensitivity by disposing a light generator (backlight unit) on the back surface of the TFT active matrix substrate 10′ and radiating light to the TFT active matrix substrate 10′ from the light generator.
However, when it is contemplated to apply this type of the radiation image detection device as, for example, a medical X-ray image detection device, the arrangement disclosed in JP-A No. 2004-33659 is disadvantageous in that sensitivity stability and remaining image characteristics are insufficient.